This invention relates to methods for molding and impact resistant automotive parts such as bumper beams produced thereby.
There is a need for automotive parts which are impact resistant by remaining in one piece after high speed impact. Such an automotive part is a bumper beam.
There are numerous requirements for automotive bumper beams both in North America and Europe. These requirements differ depending on whether there are for low speed impacts, high speed impacts, insurance requirements, etc.
For example, for low speed impacts the following are detailed requirements:
US Federal regulations REG 581: bumper standard. 5 impacts are required:
2 longitudinal pendulum impacts at 2.5 mph (at two heights between 16 and 20 inches);
2 corner pendulum impact (one on each corner) at 1.5 mph; and
1 longitudinal barrier at 2.5 mph.
After the 5 impacts, the requirements on the vehicle are shown in 581.5 c of the regulation.
Canada Safety Standards: Bumper passenger car CMVSS 215. 4 impacts are required:
2 longitudinal pendulum impacts at 5 mph (at two heights between 16 and 20 inches;
1 corner pendulum impact (one on each corner) at 3 mph; and
1 longitudinal barrier at 5 mph.
After 4 impacts, the requirements are the same as FED REG 581 with the important exception of requirement of FED REG 581.5c8 (no separation of polymeric coatings and permanent deviations except on bumper).
European Requirements (ECE 42). Pendulum impact at 4 km/h. Consequently, for low speed impacts, the beam must absorb energy by elastic deformation (deflection). Its rigidity is tuned to limit the deflection to the vehicle requirements.
For insurance purposes, the following are detailed requirements.
Europe: Danner
Impact at 15 km/h against a wall with 40% overlap. The goal is to reduce repair costs by limiting the degradation to the bumper. Absorbers are added between the bumper beam and the rails to protect the rails during impact. For Danner requirements, the beam+ absorber must be crushed progressively to absorb the impact energy and protect the rails.
US Requirements IIHS: Four 5 mph Crash Tests to Assess Bumper Performance
Front into flat barrier
Front into angle barrier
Rear into flat barrier
Rear into pole (7 inch diameter)
For high speed impact, the following are detailed requirements.
US Requirements: FMVSS no208
Full frontal crash against a perpendicular rigid barrier at 30 mph with unrestrained and belt restrained 50th percentile Hybrid III male dummy. The injury criteria include threshold criteria for the head, chest deceleration, chest deflection, and femur lower leg.
European: EU Directive 96/79 EC
Impact speed is 56 kph (35 mph);
Impact object is fixed deformable barrier;
Vehicle frontal overlap with barrier: 40% overlap of the vehicle width directly in line with the barrier face;
Dummy type: belt restrained, 50th percentile Hybrid III male;
Injury criteria: same threshold criteria and in addition, viscous criteria, the neck, the knee, lower leg bending (tibia index), foot/ankle, compression, and compartmental intrusion.
Consequently, for high speed impact it is important that the bumper beam distributes the load and is still in one piece attached to the rails after impact.
Other requirements are:
Pedestrian Impact: Lower leg impact at 40 kph. Three criteria are used: tibia deceleration should be less than 150 g, knee bending angle should be less than 15xc2x0 and knee shear displacement should be less than 6 mm.
Airbag Deployment: The beam should be stiff enough to trigger the airbag at 30 kph.
French Patent No. 2,749,535 discloses a process to manufacture a part in which glass fibers are adequately wetted by thermoplastic material so that parts can be molded with a better strength, stiffness and impact resistance than GMT (Glass mat thermoplastics) parts, such as bumper beams, for a given weight.
French and European patent application 99400421.6 discloses a bumper beam designed for small parking impacts (4 km/h), insurance requirements (Danner impact at 15 km/h), low weight (as compared with metallic solutions) and reduced cost. The beam is made of a profile that contains at least one polymeric material in which the profile has xe2x80x9cconesxe2x80x9d in the direction of the vehicle to attach the beam to the car.
Referring now to FIGS. 1-3, there is schematically illustrated a process for molding a bumper beam, generally indicated at 10 (FIG. 3), in accordance with the above-noted French Patent No. 2,749,535. As illustrated in FIG. 1, to mold the beam 10 six blanks are provided (FIG. 1): two blanks 12 of EMIR (that contain Twintex, manufactured by Vetrotex France. Twintex includes woven mats made of tows that contain both glass and polypropylene fibers); and four blanks 14 of GMT. The EMIR blanks 12 include outer layers of Twintex. The inner layers of EMIR may include a central glass mat layer sandwiched between polypropylene layers.
Preferably, the EMIR blanks 12 are made on a double belt press starting with 7 layers of materials. From top to bottom: Twintex (woven 4/1, 60 wt % glass, 920 g/m2), PP film, glass mats, extruded PP layer, glass mats, PP film and Twintex. The GMT in the center (i.e., the layers other than the Twintex layers) contains 30 wt % glass. The resulting EMIR blank 12 that is obtained contains 42 wt % glass and is 5 mm thick. The tows of glass fibers,are in contact (comingled) with thermoplastic material, where the fibers in each tow are wetted by the thermoplastic material in the tow. The dimensions of the EMIR blanks 12 are 1000 mmxc3x97125 mm. The blanks 14 of GMT contain 30 wt % glass and their dimensions are 166xc3x97360 mm. Their thickness is 3.7 mm.
The six blanks are heated in an oven. A robot stacks two blanks 14 of GMT, two blanks 12 of EMIR and two blanks 14 of GMT. The two stacks of GMT are put on top of the EMIR stack (on each side) with 30% overlap as shown in FIG. 2.
The assembly is transferred into a press or mold and stamped to form the bumper beam 10 illustrated in FIG. 3. The welding between the GMT blanks 14 and the EMIR blanks 12 is adequate. The GMT at the center of the EMIR blanks 12 flows to fill attachment portions 16 of the bumper beam 10. A central portion 19 of the beam 10 includes the resulting thermoplastic reinforced fiber structure 18. The attachment portions 16 include apertures 20 formed through cone portions (as illustrated in French and European patent application 99400421.6) for attachment of the bumper beam 10 to an automotive vehicle.
The resulting bumper beam 10, while satisfying parking and insurance requirements, does not satisfy high speed requirements because the cone portions by which the beam 10 is attached to rails of a vehicle are made of GMT and cannot survive such impact.
Consequently, it is desirable to have a bumper beam that can:
absorb low speed impact by elastic deflection;
absorb Danner impact (if required) by progressive crush of molded-in cone absorbers; and
insure a link between rails and load distribution during a high speed crash.
An object of the present invention is to provide a method for molding and an impact resistant automotive part such as a bumper beam produced thereby wherein the resulting bumper beam addresses both U.S. and European requirements (including high speed requirements) for bumper beams.
Another object of the present invention is to provide a method for molding and an impact resistant automotive part such as a bumper beam produced thereby wherein the bumper beam contributes to energy absorption during high speed impacts. During high speed impact, it is important that the beam remains in one piece and attached to the rails in order to distribute the impact load on a maximum area.
In carrying out the above objects and other objects of the present invention, a method is provided for molding an impact resistant automotive part adapted to be attached to an automotive vehicle at a pair of attachment locations spaced a predetermined distance apart. The method includes providing a plurality of blanks of material including at least one layer having tows of fibers, heating the plurality of blanks, and stacking the plurality of blanks to form a stack of blanks. The method further includes stamping the stack to form the automotive part having a pair of attachment portions spaced the predetermined distance apart. The tows of fibers are wetted by a resin material to form at least one thermoplastic reinforced fiber structure. The at least one thermoplastic reinforced fiber structure at least partially forms the pair of attachment portions and continuously extends between the attachment portions to link the attachment portions.
Preferably, the resin is polypropylene.
Also, preferably, the tows are woven.
The attachment portions have inner and outer surfaces and wherein two thermoplastic reinforced fiber structures at least partially form the attachment portions at the inner and outer surfaces.
Each of the two thermoplastic reinforced fiber structures may be formed from a single-layer blank.
Alternatively, each of the two thermoplastic reinforced fiber structures is formed from a multi-layer blank.
The tows may be aligned to improve part stiffness or may be unidirectional, wherein the unidirectional tows are attached together to preserve tow alignment during molding.
The woven fibers may be unbalanced.
Preferably, each of the attachment portions is cone-shaped.
The plurality of blanks typically include a plurality of blanks of glass mat thermoplastics where at least one of the blanks includes a glass mat layer and at least one layer of thermoplastic material.
The fibers are typically glass fibers.
Further in carrying out the above objects and other objects of the present invention, an impact resistant automotive part molded from a plurality of blanks is provided. The automotive part is adapted to be attached to an automotive vehicle at a pair of attachment locations spaced a predetermined distance apart. The automotive part includes a central shock-absorbing portion and a pair of attachment portions connected to the central shock-absorbing portion and spaced the predetermined distance apart. The automotive part also includes at least one thermoplastic reinforced fiber structure which at least partially forms the central shock-absorbing portion and the pair of attachment portions and continuously extends between the attachment portions to link the attachment portions.